This invention relates to metal finishing and particularly to improved devices and methods for microfinishing metal surfaces using in-process gauging techniques, and for holding and guiding microfinishing shoes.
Numerous types of machinery components require carefully controlled surface finishes in order to perform satisfactorily. For example, surface finish control, also referred to as microfinishing, is particularly significant in relation to the machining of journal bearing and cam surfaces such as are found on internal combustion engine crankshafts, camshafts, power transmission shafts, etc. For journal bearings, very accurately formed surfaces are needed to provide the desired hydrodynamic bearing effect which results when lubricant is forced under pressure between the journal and the confronting bearing surfaces. Improperly finished bearing surfaces can lead to premature bearing failure and can also limit the load carrying capacity of the bearing.
Currently, there is a demand for more precision control of journal bearing surfaces by internal combustion engine manufacturers as a result of greater durability requirements, higher engine operating speeds (particularly in automobiles), the greater bearing loads imposed through increased efficiency of engine structures, and the desire by manufacturers to provide "world class" quality products.
Significant improvements in the art of microfinishing journal bearing surfaces have been made by the assignee of the present application, the Industrial Metal Products Corporation (hereinafter "IMPCO"). IMPCO has produced a new generation of microfinishing equipment and processes referred to as "GBQ" (an abbreviation for "Generating Bearing Quality" and a trademark of IMPCO). The machines have microfinishing shoes which clamp around the journal with rigid inserts that press an abrasive coated film against the bearing surface. IMPCO's GBQ machines and processes are encompassed by U.S. Pat. No. 4,682,444, which is hereby incorporated by reference. The new generation IMPCO machines and processes have been found to provide excellent microfinishing surface quality as well as having the ability to correct geometry imperfections in bearing surfaces which are generated through grinding processes which precede microfinishing.
This specification is directed to further refinements in microfinishing machines and processes in which in-process gauging devices and techniques are employed. In accordance with this invention, size control gauging shoes are provided which continuously measure the diameter of the journal surface. The size control shoe is used in conjunction with a microfinishing shoe on a journal surface, so that, as the workpiece is rotated with respect to the shoes causing the abrasive film to remove material, the size control shoe continuously measures journal diameter. The diameter information is used to stop material removal once the desired diameter is reached. A workpiece having a number of journal surfaces such as a multi-cylinder internal combustion engine crankshaft would preferably have individual sets of size control and microfinishing shoe assemblies engaging each journal simultaneously. When the size control shoe provides an output indicative of a desired diameter for that journal, the pressure applied by the microfinishing shoe against the abrasive film on that journal is relieved while machining continues on the others until the correct diameters are reached for each journal.
Gauging devices for this application must be accurate, durable, and be able to accommodate significant workpiece "wobble" during rotation caused by eccentricity and/or lobing of the journal. In order to facilitate use, an in-process gauge for microfinishing would preferably be attached to conventional microfinishing shoe mounts, thus facilitating simple retrofit applications. Moreover, for use in gauging journal surfaces on crankshafts, the device must not extend beyond the axial ends of the journal where interference with the crankshaft would occur.
Numerous types of workpiece diameter in-process gauge devices are known according to the prior art. For example, various optical techniques have been employed in the past for gauging applications. These devices are not, however, well suited for microfinishing use since they are subject to reliability and accuracy problems due to the severe operating environment where they would be exposed to intense vibration, high temperatures, and contamination by cutting fluids, machining grit, etc. For these reasons, mechanical contact gauges are best suited for microfinishing applications of the type described above. Since many diameter gauges contact the workpiece at two diametrically opposite points, one design approach would be to use a pair of gauges for detecting the position of each contact probe with respect to the support structure, and using their outputs to calculate workpiece diameter. Such systems are, however, not favored since the use of two separate gauging devices gives rise to compound errors, high cost and complexity, etc.
In accordance with this invention, numerous embodiments of size control shoes are provided which enable accurate diameter measurements of journaled surfaces and use a single measuring gauge carried by a conventional microfinishing shoe hanger.
Microfinishing tooling such as that described previously is mounted to a microfinishing machine which positions the tools in contact with the workpiece surface, applies the desired pressure on the tooling and in many applications, allows the tooling to follow an orbital path of the workpiece journal during microfinishing. Presently available microfinishing machines perform these functions in an acceptable manner but have the disadvantage that in order to follow the orbital path of a workpiece surface, such as the rod journals of an internal combustion engine crankshaft, they must be specially set up for this workpiece configuration and require significant reworking to enable the machine to be used with workpieces of other configurations. Accordingly, it is another object of the present invention to provide a microfinishing machine which provides a large degree of flexibility enabling it to be used with workpieces of varying configurations without extensive reworking.